It is typically advised that you have skin surveillance on a yearly basis. Your primary care physician or dermatologist can perform this yearly assessment. However, you should also perform frequent self-exams to keep a close eye on any lesions or marks that you are aware of. Here are some skin lesions that you may encounter.
Actinic Keratosis
These lesions can be raised, scaly, and feel rough to touch. They may come and go and at times patients may notice that the rough surface falls off only to return in a few days or weeks. They mostly appear in sun-exposed areas of the skin and may increase the risk of developing skin cancers.
Basal Cell Carcinoma
The lesions usually have a pearly appearance with small blood vessels coursing through them. They might have a centrally located dimple and at times can present as a non-healing ulcer. They are firm to touch and are usually non-tender. The can continue to slowly grow in size and cause damage to surrounding structures.
Squamous Cell Carcinoma
Early versions of these tumors can appear very similar to Actinic Keratosis. They are typically red in appearance and have a scaly and rough texture. As they become more advanced they can have a non-healing ulcer, become tender and even bleed. These tumors invade the surrounding structures and can spread to distant parts of the body.
Malignant Melanoma
The appearance of these tumors varies. They are typically pigmented lesions that have changed in their characteristics. As moles and other pigmented lesions can be mistaken for these, below are some of the criteria used to determine if a lesion is likely to be malignant or not.
A (Asymmetry) – If the lesion is asymmetrical it is more likely to be cancerous than one that is perfectly symmetrical. To determine this you can imagine a line down the middle and if the two sides are relatively similar it is less likely to be malignant.
B (Border) – A lesion that has irregular borders is more likely to be cancerous than one that has regular, circular borders.
C (Color) – Uniform color of a lesion is desirable. A physician should look at any lesion with multiple pigmentations, as it is more likely to be malignant.
D (Diameter) - If the diameter of a lesion is greater than 1cm (half an inch), or has recently changed in size, this requires examination by a physician.

Source: NCI Visuals Online. Skin Cancer Foundation.
http://visualsonline.cancer.gov/about.cfm
When to see my physician:
What to do?
If you encounter any of the above situations, you should not panic. You should seek the advice of a qualified physician. This could be your primary care physician, your dermatologist, or facial plastic surgeon.